Get location with GeoClue2

Closes #8772

See merge request gajim/gajim!164

New JoinGroupchat/StartChat Dialog

See merge request gajim/gajim!161

- Complete rewrite of the old Groupchat dialog
- Has now a "minimal" mode, which is used if we have all infos for joining except the nickname and if we want to bookmark
- Handle xmpp uris received via command line

Clients should only upload square sized avatars

argument)

Fix appearance of status icon in MATE

Closes #8757

See merge request gajim/gajim!163

Tested in Debian testing (Buster) with gtk2 based MATE 1.12,
gtk3 based 1.16 and 1.18.

Moreover the used environment variable is depreacated already in 1.12:
$ echo $MATE_DESKTOP_SESSION_ID
this-is-deprecated

Fixes #8757

refactor the way we call SQL

See merge request gajim/gajim!162

used (-xyz instead of +xyz)

implement XEP-0156

Closes #5795

See merge request gajim/gajim!154

Refactor SpellChecker

See merge request gajim/gajim!159

- use Gspell instead of GtkSpell, it seems to have alot less problems
and needs less code

New version scheme

Also log the offending JID on avatar decoding issue

See merge request gajim/gajim!158

We changed the version format

Mac and Windows dont have dbus available

Fix invalid dev version string

See merge request gajim/gajim!157

Desktop files: add information for translators

See merge request gajim/gajim!156

Create desktop and appdata files in build directory

See merge request gajim/gajim!155